a. Field of the Invention
The present invention pertains to concrete mixing plants and specifically to a chemical dispensing apparatus of a concrete mixing plant.
b. Description of the Background
Concrete batch plants measure and dispense cement, aggregate, and water into mixing drums. Often, the mixing drums are mounted on a truck for delivery at a jobsite. In many cases, special chemicals are mixed into the concrete to give the concrete special properties. For example, colorants, plasticizers, anti-freezing agents, accelerants, retarding agents, stabilizers, water reducers, and other chemicals may be added to the concrete to impart specific properties to the batch of concrete. Many different chemicals are used commercially in the concrete industry.
Chemicals may be required to achieve the structural performance of each batch of concrete. Because a substandard batch of concrete may mean structural failure of a building or structure, it has become common practice to have a concrete batch plant operator visually verify that the proper amounts of chemical additives have been added to each batch of concrete. Typically, the operator fills a container to the appropriate level of chemical and verifies the amount with a sight glass. The operator verifies that the required amount of chemical has been added by checking that the sight glass has changed to “0” level.
There are several problems with the standard method of chemical measuring and dispensing. Any manual process is prone to error. In the rush to produce many batches of concrete, it is easy for an operator to overlook a chemical additive or mis-measure the amount added to a specific batch. Another problem is that the chemicals may be added at different sequences of the batch preparation, causing a potential for overlooking the injection of a chemical.
Highly viscous chemicals can present another problem in that the level of fill at the sight gauge may not be indicative of what was actually dispensed in the measurement container. This will leave a false measurement and some question about the integrity of the system.
In some mixing plants, if a batch of concrete is being mixed and a problem occurs with the chemical dispensing, the batch may not be able to be stopped. A batch that is incorrectly mixed may have to be discarded in its entirety, causing a waste of time and materials.